Several students around the Washington region have been injured or killed in attacks that have come at a time when police say risk is high and they are they are extra-vigilant: as students are returning to school from summer vacation.

-- A 15-year-old boy brought a shotgun to school on Aug. 27, the first day of classes at Perry Hall High School in Baltimore County, and started firing the weapon inside the cafeteria, striking a 17-year-old student, police said. The alleged shooter was indicted on 29 counts, including nine counts of attempted murder.

-- A 15-year-old boy was stabbed multiple times near Northwestern High School in Prince George's County on Sept. 5. Police said two 17-year-olds approached and fought the 15-year-old, who was repeatedly stabbed with an ice pick. The fight stemmed from a dispute involving the victim's cousin that occurred the day before, according to police.

Stop it before it starts
> Tips from students, parents or teachers who notice something brewing in their classrooms are the best leads police have to help prevent a violent act before it occurs, according to Officer Anna Walker of the Montgomery County police.

-- Marckel Ross, 18, was shot and killed in Capitol Heights while he was wearing his school uniform and walking to Central High on Sept. 11. Police have not made an arrest in the case.

-- On Wednesday, an 18-year-old student was shot multiple times by another student outside Coolidge High School in Northwest D.C., police said. Following a verbal altercation that occurred during the school day, a the shooter left the school and returned with a gun as classes let out, police said.

These violent encounters have come as students are returning to the routines of classes and after-school activities. The shootings and stabbings have been isolated incidents, but authorities say violence in schools frequently starts with disagreements that occur in neighborhoods -- often during the summer months -- that spill over into schools once students are forced back together in close quarters.

Police working in school systems must be vigilant during the first few weeks and months of a new school year in order to keep track of disputes that could lead to violent, criminal acts, according to Officer Anna Walker, a Montgomery County school resource officer at John F. Kennedy and James Hubert Blake high schools.

"Some of these kids live in the same neighborhoods and may not like one another for one reason or another," Walker said. "When they meet [at school], they think, 'We're closer together now, you're looking at me funny, and I don't like you because of something you did over the summer.' "

Officers work to monitor activities involving youth over the summer months to try to prevent any carry-over into schools, according to Charnette Robinson, commander of the school safety division of the District's Metropolitan Police Department.

At the beginning of the school year, students are in a transition between the less controlled environment of summer break and the more rigid structures of school and classes, said Sgt. Courtney Ballantine, who supervises Alexandria's school resource officers.

"It's like an adjustment period when school starts," Ballantine said, adding that students are more likely to act out in the first few weeks of the school year, when they are testing their boundaries.

Safety experts encourage communication among students, community members and authorities. Catherine Bradshaw, a deputy director of the Johns Hopkins Center for the Prevention of Youth Violence, said that students need to trust officers in order to come forward with their concerns and tips about disputes in school.

Examiner Staff Writer Ben Giles contributed to this report.